Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2015

The following table represents the fair value hierarchy based upon three levels of inputs, of which Levels 1 and 2 are considered observable and Level 3 is unobservable, for our financial assets and liabilities measured at fair value (in thousands):

	December 31, 2015						December 31, 2014
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets:
Cash equivalents:
Money market funds	$	35,730	$	—	$	35,730	$	9,785	$	—	$	9,785
Commercial paper		—		63,890		63,890		—		12,248		12,248
Short-term investments:
Corporate debt securities		—		31,253		31,253		—		88,494		88,494
Municipal bonds		—		2,763		2,763		—		9,945		9,945
U.S. government agency bonds		—		16,201		16,201		—		11,313		11,313
Asset-backed securities		—		11,443		11,443		—		10,336		10,336
Total	$	35,730	$	125,550	$	161,280	$	9,785	$	132,336	$	142,121

Carrying Value and Estimated Fair Value of Debt

We have chosen not to measure our debt at fair value, with changes recognized in earnings each reporting period. The following table indicates the carrying value and estimated fair value of our debt as of the indicated periods (in thousands):

	December 31, 2015				December 31, 2014
	Carrying Value		Fair Value		Carrying Value		Fair Value
Credit Agreement (carrying value including current maturities)	$	142,500	$	142,500	$	120,000	$	120,000
Convertible debt (par value)		150,000		237,900		150,000		178,920

Allowance for Doubtful Accounts Receivable

The activity in our allowance for doubtful accounts receivable is as follows (in thousands):

	2015			2014			2013
Balance, beginning of year	$	3,323		$	2,359		$	3,147
Additions (reductions) to expense		533			1,406			(354	)
Write-offs		(318	)		(465	)		(280	)
Recoveries		89			-			-
Other		(27	)		23			(154	)
Balance, end of year	$	3,600		$	3,323		$	2,359

Reconciliation of the Basic and Diluted EPS denominators

The reconciliation of the basic and diluted EPS denominators related to the common shares is included in the following table (in thousands):

	2015		2014		2013
Basic weighted-average common shares		31,051		32,449		32,117
Dilutive effect of common stock options		—		—		1
Dilutive effect of restricted common stock		624		569		550
Dilutive effect of 2010 Convertible Notes		1,633		717		205
Dilutive effect of Stock Warrants		130		1		—
Diluted weighted-average common shares		33,438		33,736		32,873